This invention relates to a vehicle communication control apparatus which is mounted on a vehicle and controls communication among electronic appliances in a vehicle (hereinafter referred to as vehicle electronic appliances) such as a navigation system unit, an ABS (antilock brake system) unit, and the like.
Heretofore, reduction in this size of wire harnesses and lightening of a weight of a vehicle have been carried out by interconnecting a plurality of vehicle electronic appliances mounted on a vehicle through multiplex communication cables to provide a vehicle with high performance. Currently, since various kinds of vehicle electronic appliances are mounted on a vehicle, vehicle electronic appliances which are integral to each other are assembled together in a group and the vehicle electronic appliances in each group are interconnected through multiplex communication cables to form a plurality of groups of networks in a vehicle. The respective groups of networks are interconnected by vehicle communication control apparatuses which serve as a so-called gateway to effect communication among the respective groups of networks.
This manner can not only speed up communication in each group of networks but also effect communication among the respective groups of networks, since the vehicle electronic appliances which are integral to each other in each group of networks are interconnected by relatively short cables and the respective groups of networks are interconnected by the vehicle communication control apparatuses.
Heretofore, in order to diagnose a trouble in vehicle electronic appliances in a group of networks, a trouble diagnosis tester is connected to the group of networks and is brought into access each vehicle electronic appliance to start a self test function of each appliance or to directly read and write a register in the appliance. Then, the trouble diagnosis tester analyzes results such as read and write of the self test or register and determines existence and position of trouble in each vehicle electronic appliance.
However, in the case where the trouble diagnosis tester changes an access from one group of networks to the other group of networks, the tester cannot effect the access to the vehicle electronic appliances in the other group of networks unless both groups of networks are in a condition for receiving a diagnostic check since a vehicle communication control apparatus merely serves as a gateway. Consequently, it takes much time to commence the trouble diagnosis.
If either group of networks operates at a lower speed, it will take great deal of time from trouble diagnosis of the vehicle electronic appliances to transmission of the diagnostic results, since both groups of networks are occupied by the trouble diagnosis tester during trouble diagnosis. Since the other group of networks which operates at a high speed is occupied by the tester in the meantime, efficiency of utilization of a group of networks in trouble diagnosis of vehicle electronic appliances will be lowered.